Reaction injection molding (RIM) is a versatile process by which elastomeric and thermoset parts can be fabricated. The RIM process involves high pressure impingement mixing of a polyisocyanate stream (A-side) and an active-hydrogen containing isocyanate-reactive stream (B-side) followed by immediate injection into the closed mold. The primary appeal of this process lies in its inherently high productivity. One factor which limits productivity, however, is the necessity to spray the molds with external mold release prior to each injection. This is a time-consuming task and often has a negative environmental impact. This difficulty can be overcome by the incorporation of an internal release agent into the formulation via one of the two streams to significantly increase the number of molding cycles which can be accomplished between mold release sprayings.
The use of metallic soaps as release agents has been known for a long time. Zinc stearate, in particular, is known to be soluble in aliphatic amines, such as the polyether polyamines and ethylenediamine-initiated polyols. This is the basis for its use as an internal mold release (IMR) agent in RIM. If zinc stearate is simply dispersed as a fine powder in polyol blends, it does not dissolve and does not act as a release agent. Various patents teach that zinc soaps can be compatibilized or dissolved in polyol blends with amines, enamines, ketimines or salts of amidines or guanidines, and that excellent releasability of the subsequent RIM parts will result.
While the IMR approach is commercially applied, there remains significant shortcomings to the currently available IMR systems. The amine-solublized metallic soaps, which are most commonly used in this application, have been implicated in reactivity and/or physical property deficiencies for the RIM elastomers in which they are used. Furthermore, the high melting points and limited solubilities of the metallic soaps make them prone to precipitation in the RIM processing equipment, necessitating replacement of the piping regularly.
Another class of IMR agents which has been reported includes fatty acidic materials. WO 84/03288 discloses the optional use of fatty acids in addition to metallic soaps plus amines. U.S. Pat. No.4,220,727 discloses the use of fatty acids plus their alkali metal salts. U.S. Pat. No. 4,130,698 discloses the use of fatty acids plus their esters. Salts of amines with fatty acids are taught in U.S. Pat. Nos. 3,726,952; 3,993,606 and 4,098,731. U.S. Pat. No. 3,726,952 discloses amines with fatty acids in which the amines include primary amines or amines which contain ester or amide groups. In U.S. Pat. No. 3,993,606 the amines include primary, secondary or tertiary amine-bearing polysiloxanes. In U.S. Pat. No. 4,098,731 the amines include tertiary amines with a tertiary amine nitrogen to carbon ratio between 1:3 and 1:12 and having no ester or amide groups present. The effect of acids on the NCO--OH reaction is to retard the rate sufficiently to cause green strength problems. Therefore these approaches cannot be used in conventional RIM systems using traditional tin catalysts.
The search for IMR agents which are liquids without the possibility of solidifying led to the development of special silicone fluids for this application. U.S. Pat. No.4,076,695 discloses certain carboxy-functional silicone fluids as IMR agents for RIM, including Dow Corning's commercial carboxy-functional silicone fluid Q2-7119, which has the following general formula: ##STR1##
In general, acids have a deleterious effect on the green strength of aryldiamine-extended polyurethaneurea RIM systems due to a general deactivation of the tin catalyst. Thus, higher than normal levels of tin catalysts are needed when acids are present. Due to the sulfur atom, alpha to the carbonyl group, Q2-7119 is a much stronger acid than a typical fatty acid, such as lauric acid. Therefore, when T-12 (dibutyltin dilaurate) and Q2-7119 are in the same polyol blend, the equilibrium reaction involving the two components leads to a gelled silicone salt. This gelation results from a crosslinking reaction between the trifunctional silicone and the difunctional tin salt. The result is that the system exhibits extremely poor green strength which cannot be corrected by the addition of more tin catalyst.
Attempts to dissolve this problem include the following:
U.S. Pat. No. 4,379,100 discloses the use of a 3-stream approach to RIM molding where the Q2-7119 is delivered dispersed in polyol containing no tin catalyst. The other two streams are the normal A and B sides of RIM technology. The A side is isocyanate and the B side is a blend of polyol, diamine chain extender, surfactants and tin and amine catalysts.
U.S. Pat. No. 4,420,570 discloses that the tin catalyst can be placed in the A side. Gelation is avoided, but high levels of catalysts are still needed for adequate green strength. Furthemore, placing the tin catalyst in the isocyanate increases the moisture sensitivity and susceptibility to side reactions, such as allophonate formation, leading to gelation of the isocyanate.
U.S. Pat. No. 4,396,729 discloses replacing the polyether polyol and the tin catalyst with polyether polyamines which require no tin catalyst. The result is polyurea RIM, and Q2-7119 can be used with no chemical modification or 3-stream approach.
U.S. Pat. No. 4,472,341 discloses that the acid groups on Q2-7119 can be converted to amides by reaction with amines or to esters by reaction with alcohols or epoxides yielding nonacidic IMR silicones. These materials have been shown to cause paintability problems. In addition, they have been seen to interfere with polyol nucleation so that low part densities cannot be achieved. In extreme cases, large voids are found in the parts due to coalescence of bubbles.
U.S. Pat. No. 4,477,366 discloses that Q2-7119 can be dispersed on the isocyanate side by using a nonisocyanate-reactive silicone as a dispersing and inhibiting agent.
U.S. Pat. No. 4,487,912 discloses the use of the reaction products of fatty cyclic anhydrides with primary or secondary amines, including distearylamine as IMR agents.
U.S. Pat. No. 4,585,803 discloses that salts of Q2-7119 can be made with Group IA, IB, IIA, IIB, aluminum, chromium, molybdenum, iron, cobalt, nickel, tin, lead, antimony or bismuth. These salts are then compatiblized in the B-side blend with certain tertiary amines. In practice, these salts are extremely viscous or gelatinous in nature and do not disperse well into the polyol.
U.S. Pat. Nos. 4,764,540 and 4,789,688 disclose that salts of Q2-7119 can be made with amidines and guanidines, such as tetramethylguanidine, to yield neutralized forms of the silicone which would not gel tin catalysts. Waxy amidines such as the imidazolines from stearic acid and ethylenediamine derivatives were cited as particularly efficacious for release.
U.S. application Ser. No. 07/992,360, filed 16 Dec. 1992 discloses as the internal mold release (IMR) additive a composition consisting essentially of the reaction product of a tertiary amine, such as triethylenediamine (TEDA), with an epoxide reacted in the presence of a carboxy-functional siloxane such as Q2-7119. Application testing of these ionic silicone IMRs proves that they are release agents which do not gel tin catalysts. Excellent green strength and release is achieved using these release agents with conventional tin catalysts in RIM systems which are based on t-butyl toluenediamine (TBTDA) however, these new derivatives of Q2-7119 do not give good green strength in diethyl toluenediamine (TETDA) based RIM elastomer formulations with conventional tin catalysts even though no gellation of tin catalyst is seen.
U.S. Pat. No. 4,742,090 describes the use of bismuth carboxylates as catalysts for polyurethaneureas made from the reaction of polyisocyanates with blends of aromatic diamines with polyols.
JP 2,262,727 teaches the use of these bismuth salts and RIM systems based on TBTDA and IMR packages consisting of salts of fatty acids with tertiary amines.
JP 2,262,728 teaches the use of the bismuth salts for RIM systems based on tri-isopropyl-metaphenylenediamine and IMR packages consisting of salts of fatty acids with tertiary amines.